Development of Multilayer Models of Globular Star Clusters and Study of Their Evolution

Usually, models of globular star clusters are created by analyzing their luminosity and other observation parameters. The goal of this work is to create stable models of globular clusters based on the laws of mechanics. It is necessary to set the coordinates, velocities and masses of the stars so that as a result of their gravitational interaction the globular cluster is not destroyed. This is not an easy task, and it has been solved in this paper. Using an exact solution of the axisymmetric gravitational interaction of N-bodies, single-layer spherical structures were created. They are combined into multilayer models of globular clusters. An algorithm and a program for their creation is described. As a result of solving the problem of gravitational interaction of N bodies, evolution of 5-, 10-, and 15-layer structures was studied. During the inter-body interaction, there proceeds a transition from the initial specially organized structure to a structure with bodies, uniformly distributed in space. The number of inter-body collisions decreases, and the globular cluster model passes into the stable form of its existence. The collisions of bodies and the acquisition of rotational motion and thermal energy by them are considered. As a result of the passage to scaled dimensions, the results were recalculated to the conditions of globular star clusters. The periods of rotation and the temperatures of merged stars are calculated. Attention is paid to a decreased central-body mass in the analyzed models of globular star clusters.

Theoretical study of small Mo clusters and molecular nitrogen adsorption on Mo clusters

This paper studies the small molybdenum clusters of Mon （n=2 8） and their adsorption of N2 molecule by using the density functional theory （DFT） with the generalized gradient approximation. The optimized structures of Mon clusters show the onset of a structural transition from a close-packed structure towards a body-centred cubic structure occurred at n = 7. An analysis of adsorption energies suggests that the Mo2 is of high inertness and Mo6 cluster is of high activity against the adsorption of N2. Calculated results indicate that the N2 molecule prefers end-on mode by forming a linear or quasi-linear structure Mo-N-N, and the adsorption of nitrogen on molybdenum clusters is molecular adsorption with slightly elongated N-N bond. The electron density of highest occupied molecular orbital and lowest unoccupied molecular orbital, and the partial density of states of representative cluster are also used to characterize the adsorption properties of N2 on the sized Mon clusters.

Theoretical Studies on the Stabilities and Hydrogen Bond Actions of (H_2O)_n Clusters

The stable configurations and hydrogen bond nature of （H2O）n clusters （n = 3-6） have been investigated by the B3LYP method at the 6-31＋＋g^＊＊ level. Upon calculation, four conclusions have been drawn： （1） In the （H2O）3-5 clusters, cyclic configurations were confirmed to be the most stable. But in the （H2O）3-4 ones, only cyclic configurations could be observed. From n = 5 （（H2O）5 clusters）, three-dimensional configuration could be found： （2） In the （H2O）6 clusters, all configurations are inclined to be three-dimensional except the most stable configuration which is cyclic; （3） The stable order of （H2O）6 clusters indicates that it is the arrangement of hydrogen bond that plays a decisive role in the cluster stabilities, the zero-point energy is also important, and cluster stabilities are independent on the number of hydrogen bonds; （4） There exist strong cooperativity and superadditivity in the （H2O）n clusters.

Density functional investigation on structural and electronic properties of small bimetallic Pb_(n)Ag_(n)(n=2–12)clusters

Structural and electronic properties of PbnAgn(n=2–12)clusters were investigated by density functional theory with generalized gradient approximation at BLYP level in DMol3 program package.The optimized bimetallic PbnAgn(n=2–12)clusters were viewed as the initial structures,then,those were calculated by ab initio molecular dynamics(AIMD)to search possible global minimum energy structures of PbnAgn clusters,finally,the ground state structures of PbnAgn(n=2–12)clusters were achieved.According to the structural evolution of lowest energy structures,Ag atoms prefer gather in the central sites while Pb atoms prefer external positions in PbnAgn(n=2–12)clusters,which is in excellent agreement with experimental results from literature and the application in metallurgy.The average binding energies,HOMO-LUMO gaps,vertical ionization potentials,vertical electron affinities,chemical hardnessη,HOMO orbits,LUMO orbits and density of states of PbnAgn(n=2–12)clusters were calculated.The results indicate that the values of HOMO-LUMO gaps,vertical ionization potentials,vertical electron affinities and chemical hardnessηshow obvious odd-even oscillations when n≤5,PbnAgn(n=2–12)clusters become less chemically stable and show insulator-to-metal transition with the variation of cluster size n,PbnAgn(n≥9)cluster are good candidates to study the properties of PbAg alloys.Those can be well explained by the density of states(DOS)distributions of Pb atoms and Ag atoms between–0.5 Ha and 0.25 Ha in PbnAgn(n=2–12)clusters.

Probing structural and electronic properties of divalent metal Mg_(n+1) and SrMgn (n=2–12) clusters and their anions

Divalent metal clusters have received great attention due to the interesting size-induced nonmetal-to-metal transition and fascinating properties dependent on cluster size,shape,and doping.In this work,the combination of the CALYPSO code and density functional theory(DFT)optimization is employed to explore the structural properties of neutral and anionic Mg_(n+1) and SrMgn(n=2-12)clusters.The results exhibit that as the atomic number of Mg increases,Sr atoms are more likely to replace Mg atoms located in the skeleton convex cap.By analyzing the binding energy,second-order energy difference and the charge transfer,it can be found the SrMg9 cluster with tower framework presents outstanding stability in a studied size range.Further,bonding characteristic analysis reveals that the stability of SrMg9 can be improved due to the strong s-p interaction among the atomic orbitals of Sr and Mg atoms.

A density-functional theory for (BAs) n clusters (n=1-14):structures,stabilities and electronic properties

This paper investigates the lowest-energy structures, stabilities and electronic properties of （BAs）n clusters （n=1- 14） by means of the density-functional theory. The results show that the lowest-energy structures undergo a structural change from two-dimensional to three-dimensional when n ： 4. With the increase of the cluster size （n=6）, the （BAs）n clusters tend to adopt cage-like structures, which can be considered as being built from B2As2 and six-membered rings with B-As bond alternative arrangement. The binding energy per atom, second-order energy differences, vertical electron affinity and vertical ionization potential are calculated and discussed. The caculated HOMO-LUMO gaps reveal that the clusters have typical semiconductor characteristics. The analysis of partial density of states suggests that there are strong covalence and molecular characteristics in the clusters.

Structures,stabilities,and electronic properties of GaAs tubelike clusters and single-walled GaAs nanotubes

The geometric structures, stabilities, and electronic properties of （GaAs）n tubelike clusters at up to n = 120 and single-walled GaAs nanotubes （GaAsNTs） were studied by density functional theory （DFT） calculations. A family of stable tubelike structures with a Ga-As alternating arrangement were observed when n ≥ 8 and their structural units （four-membered rings and six-membered rings） obey the general developing formula. The average binding energies of the clusters show that the tubelike cluster with eight atoms in the cross section is the most stable cluster. The size- dependent properties of the frontier molecular orbital surfaces explain why the long and stable tubelike clusters can be obtained successfully. They also illustrate the reason why GaAsNTs can be synthesized experimentally. We also found that the single-walled GaAsNTs can be prepared by the proper assembly of tubelike clusters to form semiconductors with large band gaps.

Density Functional Theory Study on the Structural and Electronic Properties of Ge(SiO_2)_n Clusters

The geometry,stability,binding energy and electronic properties of（SiO2）n and Ge（SiO2）n clusters（n = 7） have been investigated by Density functional theory（DFT）.The results show that the lowest energy structures of Ge（SiO2）n are obtained by adding one Ge on the end site of the O atom or the Si near end site of the O atom in（SiO2）n.The chemical activation of Ge-（SiO2）n is improved compared with（SiO2）n.The calculated second-order difference of energies and fragmentation energies show that the Ge（SiO2）n clusters with n = 2 or 5 are stable.

The geometry structures and electronic properties of Li_mB_n(m+n=12) clusters

The geometric structures, electronic properties, total and binding energies, harmonic frequencies, the highest occupied molecular orbital to the lowest unoccupied molecular orbital energy gaps, and the vertical ionization potential energies of small LimBn （m＋ n = 12） clusters were investigated by the density functional theory B3LYP with a 6-31 I＋G （2d, 2p） basis set. All the calculations were performed using the Gaussian09 program. For the study of the LimBn clusters, the global minimum of the B 12 cluster was chosen as the starting point and the boron atoms were gradually replaced by Li atoms. The results showed that as the number of Li atoms increased, the stability of the LimBn cluster decreased and the physical and chemical properties became more active. In addition, on average there was a large charge transfer from the Li atoms to the B atoms.

Structure and Properties of Semiconductor Microclusters Ga_nP_n(n=1-4): A First Principle Study

The possible geometrical structures and relative stabilities of semiconductor microclusters Ga\-\%n\%P\-\%n(n\%=1\_4) were studied by virtue of density functional calculations with generalized gradient approximation(B3LYP). For the most stable isomers of Ga\-\%n\%P\-\%n(n\%=1\_4) clusters, the electronic structure, vibrational properties, dipole moment, polarizability and ionization potential were analyzed by means of HF, MP2, CISD and B3LYP methods with different basis sets.

Quantum Chemical Study of Geometric Structures and Properties for Ag_nH_2S(n = 1～10) Clusters

The stable structures and stabilities of AgnH2S（n = 1-10） clusters have been calculated using the B3P86-DFT method. The results predicate that the stable geometries of AgnH2 S clusters can be got by directly adding the H2 S molecule on different sites of Agn clusters. Agn clusters would like to bond with sulfur atom and the H2 S molecules are partial to adsorb at the top site in the clusters. After adsorption, the structures of Agn clusters and H2 S molecule keep the original structures except Ag9. The binding energy of AgnH2 S is distinctly larger than that of pure Agn clusters. The second difference in energy and the HOMO and LUMO gaps of Agn and AgnH2 S exhibit an obvious odd-even oscillation, which demonstrate that the stabilities of even-numbered silver clusters are relatively more stable than the neighboring odd-numbered silver clusters. Mulliken population analysis shows that charges always transfer from the H2 S molecule to Agn clusters in all clusters.

Computational Study on Interactions between CO2 and （TiO2）n Clusters at Specific Sites

The energetic pathways of adsorption and activation of carbon dioxide (CO2) on low-lying compact (TiO2)n clusters are systematically investigated by using electronic structure calculations based on density-functional theory (DFT). Our calculated results show that CO2 is adsorbed preferably on the bridge O atom of the clusters, forming a "chemisorption" carbonate complex, while the CO is adsorbed preferably to the Ti atom of terminal Ti-O.The computed carbonate vibrational frequency values are in good agreement with the results obtained experimentally, which suggests that CO2 in the complex is distorted slightly from its undeviating linear configuration. In addition, the analyses of electronic parameters, electronic density, ionization potential, HOMO-LUMO gap, and density of states(DOS) confirm the charge transfer and interaction between CO2 and the cluster. From the predicted energy profiles, CO2 can be easily adsorbed and activated, while the activation of CO2 on (TiO2)n clusters are structure-dependent and energetically more favorable than that on the bulk TiO2. Overall, this study critically highlights how the small (TiO2)n clusters can influence the CO2 adsorption and activation which are the critical steps for CO2 reduction the surface of a catalyst and subsequent conversion into industrially relevant chemicals and fuels.

Magneto-volume effect in Fe_(n)Ti_(13-n)clusters during thermal expansion

Ab initio molecular dynamics calculations have been carried out to search for the ground state structure of Fe_(n)Ti_(13-n)clusters and measure the thermal expansion of Fe_(n)Ti_(13-n).The volume of Fe_(n)Ti_(13-n)clusters during thermal expansion is jointly determined by anharmonic interaction and magneto-volume effect.It has been found that Fe_(6)Ti_(7),Fe_9Ti_(4),Fe_(11)Ti_(2),and Fe_(13)clusters can exhibit the remarkable magneto-volume effect with abnormal volume behaviors and magnetic moment behaviors during thermal expansion.A prerequisite for the magneto-volume effect of Fe_(n)Ti_(13-n)clusters during thermal expansion has been revealed and the magnitude of the magneto-volume is also approximately determined.Furthermore,the magneto-volume behaviors of Fe_(n)Ti_(13-n)clusters are qualitatively characterized by the energy contour map.Our results shed light on the mechanism of the magneto-volume effect in Fe_(n)Ti_(13-n)clusters during thermal expansion,which can guide the design of nanomaterials with zero expansion or even controllable expansion properties.

Magnetic properties of small Fe clusters: a nonorthogonal Hamiltonian study

We calculate the magnetic properties of small Fe N clusters( N =2～7,9,13,15) by using a parameterized Hubbard tight binding spd band model Hamiltonian, with the parameters obtained from nonorthogonal Hamiltonian parameters. the average magnetic moments, and the spin polarized charge distribution within clusters are in agreement with those obtained by first principle and tight binding calculations. The effect of the nonorthogonal basis is discussed.

CdTe/CdS量子点在Nafion/羟基磷灰石膜上的电化学发光及其应用于肌红蛋白的高灵敏检测

利用羟基磷灰石(HAp)和Nafion将CdTe/CdS量子点(QDs)修饰到玻碳电极表面,研究了固定在复合膜内的CdTe/CdS量子点的电化学发光行为。相比水溶液中的量子点在裸电极上的电化学发光,CdTe/CdS修饰到复合膜内后的电化学发光更加稳定,且发光强度增加数十倍。在pH为6.5的磷酸盐缓冲溶液(PBS)中,以三丙胺(TPrA)为共反应物,基于肌红蛋白(Mb)能有效地猝灭量子点的电化学发光(ECL)强度,建立了一种灵敏度较高的检测Mb的新方法,同时我们探讨了Mb猝灭QDs电化学发光的可能机理。实验结果表明,Mb浓度在0.59 nmol/L～10.59 nmol/L范围内,分析信号lg(I0-I)/I与肌红蛋白浓度的对数lg[CMb]有良好的线性关系,检出限为0.12 nmol/L(S/N=3)。

辉光放电电解等离子体引发合成CdTe/CdS-PNIPAM复合水凝胶及荧光温敏特性

利用辉光放电电解等离子体引发制备出CdTe/CdS-PNIPAM复合水凝胶。采用红外光谱、透射电镜、差热分析和荧光光谱对其结构、形态、相转变温度和荧光性能进行表征,同时考察了水凝胶的溶胀率、温敏性能和荧光可逆行为。结果表明,CdTe/CdS量子点均匀分散,且与温敏单体通过配位结合在水凝胶网络中,复合水凝胶有良好的透明性和荧光性,相转变温度为32.5℃,复合水凝胶在20℃和40℃的荧光强度分别为1490 a.u.和20 a.u.,经5次加热-冷却循环后荧光强度变化不大,具有良好的荧光可逆性能。

（OsH_2）_n（n=1~5）团簇结构稳定性与磁学性质的理论研究

采用密度泛函理论,在广义梯度近似（GGA）下对（Os H2）n（n=1~5）团簇的可能构型进行几何参数全优化,得到基态结构,并对基态结构的平均结合能（Eb）、能量二阶差分（Δ2E）、磁矩和态密度等进行计算.结果表明：（Os H2）n（n=1~5）团簇趋向于形成空间三维结构,Os与H之间有较强的相互作用,并且Os H2的基态结构可以看作是（Os H2）n（n=1~5）团簇结构的基本组成单元;（Os H2）4团簇稳定性较好,只有（Os H2）5基态结构呈反铁磁性耦合,团簇的磁矩主要来源于Os原子的d轨道.

N-乙酰-L-半胱氨酸修饰的CdTe量子点与人血清白蛋白的相互作用

以N-乙酰-L-半胱氨酸为修饰剂,制备了水溶性的CdTe量子点(NAC-CdTe QDs)。利用荧光光谱法和等温滴定量热法(ITC)研究了NAC-CdTe QDs与人血清白蛋白(HSA)的相互作用。结果表明,NAC-CdTe QDs对HSA内源荧光具有较强的动态猝灭作用,且猝灭作用是扩散控制的。

密度泛函理论研究(CdTe)_n和(HgTe)_n团簇的基态结构和电子性质

采用密度泛函理论中的广义梯度近似对(CdTe)n和(HgTe)n(n=2～8)团簇的几何结构进行优化,计算了其能量,研究了其电子性质。结合能、最高占据轨道和最低未占据轨道的能隙计算结果表明,n=3、6是团簇的幻数;比较2种团簇的基态结构,发现2种团簇的最低能量结构不同,这可能是导致块体材料CdTe是宽带隙半导体材料,而HgTe是半金属材料的原因。

密度泛函理论研究(CdTe)_n (n=2～8)团簇的基态结构与电子性质

采用密度泛函理论中的广义梯度近似对(CdTe)n(n=2～8)团簇的几何结构进行优化,并对结合能、最高占据轨道和最低未占据轨道的能隙、垂直亲和势和二阶能量差分进行了计算.结果表明,(CdTe)3和(CdTe)6是稳定的团簇,即n=3和6是团簇的幻数.